The Secret Year by Jennifer Hubbard

Colt and Julia were secretly together for a year, and no one ever knew, not even Julia's boyfriend. Why would they-they were from two different crowds. Julia lived in her country club world and Colt . . . didn't. Then Julia dies in a car accident. Colt is devastated but can't mourn openly, and he's tormented that he may have played a part in her death. And when Julia's journal ends up in his hands, he is forced to relive their year together-just when he is trying to forget. The problem is, how do you get over someone who was never really yours to begin with?